The present invention relates generally to hitches for attaching implements to agricultural tractors and more particularly to systems and methods for controlling the draft load of an implement connected to a tractor.
One of the most common uses of agricultural tractors is to move implements through agricultural fields to cultivate and condition the soil. Implements are commonly connected to the tractor using a front- or rear-mounted three-point hitch devices or towed using a drawbar. A three-point hitch device typically comprises two bottom lift arms, to which the implement is connected in rotary manner to selectively pivot about a given hinge axis; and a top link interposed between the tractor frame and the implement to control the angular position of the implement about the hinge axis. The lift arms are moved by a further actuating cylinder (or cylinders) interposed between the tractor frame and the lift arms, movement of the lift arms raising and lowering the implement with respect to the ground. Similarly, most trailed implements include one or more wheels pivotably connected to the implement in a manner to raise and lower the implement with respect to the ground offering an alternative method for altering implement position. Movement of the lift arms and/or implement-attached wheels is used to establish implement position with respect to the ground. Three-point hitches, as well as numerous variations thereof, are well known in the agricultural industry.
It is desirable, and sometimes critical for today's arming practices, to control the quality of cultivation performed by various ground-engaging devices attached to the frame of the implement. As the frame is lowered closer to the ground, the ground-engaging devices or tools dig or cut deeper into the soil and the draft load increases. As the frame is raised higher above the ground, the ground-engaging devices dig more shallowly into the soil and the draft load decreases. Typically, the operator has a manually operable device in the cab of the tractor that is manipulated to raise and tower the implement accordingly, whether by the three-point hitch or the implement wheels. When the operator finishes manipulating the device, the implement remains in the position set by the operator, but will not, however, maintain a desired depth of engagement or implement draft load as the tractor and implement move across the ground. Changes in field contour or soil hardness cause the depth of engagement and/or the draft load to change. To maintain the implement in a position to achieve a consistent draft load or depth of engagement, the operator must periodically look rearward and observe the implement. If the implement has drifted away from the desired depth of engagement, the operator must manipulate the depth control device to reposition the implement until the desired depth of engagement is reestablished. Similarly, changes in draft load may cause the engine to be bogged down, requiring operator adjustment of implement position to avoid stalling the engine. Therefore, even in systems in which the operator can adjust the implement position, periodic or semi-constant under some field conditions, visual monitoring of the implement position and adjustment of the hitch height input device is necessary to maintain the desired depth of engagement.
Hitch control systems for three-point hitch devices alleviate the need for manual operator hitch adjustments by controlling the position of the connected implement in response to loads applied to the tractor by the implement. The control systems allow the depth of engagement to be adjusted so that a constant draft load is applied to the tractor to smooth tractor operation. Alternatively, control systems may maintain the implement ground-engaging tools at a constant depth of engagement thereby allowing the implement tools to follow field contours. Such control systems typically use one or more measuring devices to sense the draft loads applied to the hitch by the implement and then generate a control output to adjust the hitch in response to the applied loads and desired position. Measuring devices add cost to the tractor and are subjected to generally harsh environments which increase failure rates and reduce reliability. The measurements used by these systems are more an indication of the load generated by the implement, with little or no consideration of other loads applied to the tractor engine, such as loads from the PTO, auxiliary hydraulics, cab air conditioning, cooling fans and the like. Such force sensing devices are typically installed only on rear three-point hitches which limits the draft control to rear hitched implements. Drawbar trailed or front hitch mounted implements cannot, therefore, be included in the draft load control systems.
Conventional hitch control systems are also generally limited in their inputs. Information on the type of attached implement and other engine loads is typically unavailable to the control system unless manually programmed into the control system. The type of implement attached to the tractor affects the relationship between depth and pulling force, the relationship between vertical forces and horizontal forces, tension versus compression, and center of gravity changes. As with other unmonitored engine loads, improperly set control parameters can also lead to engine stalling due to overload.
One alternative approach is to measure the drivetrain torques to determine draft loads. Various torque monitoring devices have been proposed or implemented. Drivetrain torque measurements provide a more direct indication of engine load and allow indirect measurement of draft load measurement. As with direct measurement of draft loads through the tractor hitch, drivetrain torque measurement inherited many similar drawbacks, including cost, noise, failure, reliability, and capacities.
It would be a great advantage to provide a system for controlling the depth of ground engagement (implement height) and therefore the draft load imposed on the tractor by the coupled implement in a manner to maintain a constant draft load on the tractor. Further advantages would be realized if the draft load control system would function for any connected implement regardless of whether the implement is connected to a front hitch, a rear hitch, or towed by a drawbar. Still further advantages would be realized if the draft load control system received inputs from existing sensing/control systems thereby alleviating the need for dedicated sensing components. These and other advantages are provided by the draft control system described below.